Streptococcus thermophilus Ab.340 TZ enhances doxorubicin efficacy in glioblastoma cells by modulating apoptotic and survival pathways

Schematic overview of the anti-glioblastoma potential of Streptococcus thermophilus Ab.340 TZ, a probiotic strain isolated from traditional dairy products (NCBI Accession: PX207693). The bacterium, in combination with doxorubicin (DOX), was applied to U-87 MG glioblastoma cells. Cell viability was assessed using the MTT assay, showing a marked reduction in tumor cell survival while sparing normal HUVECs. Flow cytometry (Annexin V/PI) confirmed enhanced apoptosis induction in co-treated cells. Gene expression profiling by qRT-PCR revealed significant upregulation of pro-apoptotic markers ( Caspase-3, Caspase-8, Caspase-9, Bax, Fas, p53, p21 , PTEN ) and downregulation of survival/anti-apoptotic mediators ( Bcl-2, AKT, mTOR, IκB ). Collectively, S. thermophilus Ab.340 TZ potentiated DOX efficacy by reprogramming apoptotic and PI3K/AKT/mTOR signaling pathways, enabling a substantial reduction in DOX effective dose while selectively targeting glioblastoma cells. • Streptococcus thermophilus Ab.340 TZ was isolated from traditional yogurt. • The probiotic selectively reduced U-87 MG glioblastoma cell viability. • Combination of S. thermophilus and doxorubicin reduced DOX IC 50 by > 130-fold. • Co-treatment upregulated pro-apoptotic genes and downregulated AKT/mTOR/Bcl-2. • The combination induced apoptosis in GBM cells while sparing HUVECs. Glioblastoma multiforme (GBM) is the most aggressive primary brain tumor, characterized by rapid proliferation, therapeutic resistance, and poor prognosis. Doxorubicin (DOX) exhibits potent cytotoxicity but is limited by blood–brain barrier penetration and systemic toxicity. Probiotics, particularly Streptococcus thermophilus, have emerged as potential adjuvants in cancer therapy due to their selective anticancer effects. S. thermophilus Ab.340 TZ (NCBI Accession: PX207693) was isolated from 55 traditional yogurt samples and identified via 16S rRNA sequencing. U-87 MG glioblastoma cells and HUVECs were treated with the probiotic, DOX, or their combination. Cell viability was assessed by MTT assay. Molecular mechanisms were investigated using quantitative real-time PCR (qRT-PCR) for apoptosis- and survival-related genes ( Caspase-3, Caspase-8, Caspase-9, Bax , Bcl-2, PTEN, p53, p21, Fas, AKT, mTOR, IκB ). Apoptosis induction was further validated by Annexin V-FITC/PI flow cytometry. S. thermophilus selectively reduced U-87 MG viability in a dose-dependent manner (IC 50 OD 600 = 1.15, ≈1–1.2 × 10 9 CFU/mL) without affecting HUVECs (>96% viability) . DOX monotherapy had an IC 50 of 20 µg/mL, while combination therapy achieved comparable cytotoxicity at only 145 ng/mL, indicating a > 130-fold dose reduction. qRT-PCR revealed synergistic upregulation of pro-apoptotic and tumor suppressor genes ( Caspases, Bax, PTEN, p53, p21 ) and downregulation of survival mediators ( AKT, mTOR, Bcl-2 ). Flow cytometry confirmed enhanced apoptosis with minimal necrosis in combination-treated cells. S. thermophilus Ab.340 TZ acts as a potent adjuvant to DOX, reprogramming apoptosis and survival pathways, enabling substantial dose reduction, and selectively inducing apoptosis in GBM cells. These findings support the potential integration of probiotics with conventional chemotherapy to overcome chemoresistance and improve therapeutic outcomes in glioblastoma.